This invention relates to a novel dental filling composition. In particular, it relates to a dental filling composition which bonds strongly and adhesively to tooth enamel, to dentin, to dental prostheses and to preexisting dental fillings both conventional and of the present invention, in addition to forming a hard mass for space filling in dental cavities and the like.
Most conventional dental restorative filling materials have the serious disadvantage that they do not form strong or durable adhesive bonds to the natural tooth materials to which they are commonly applied, namely tooth enamel and dentin. For this reason it is standard practice to undercut cavities and boreholes before filling them, and thus to lock the moulded and set filling material mechanically in place. While undercutting inherently involves the removal of healthy tooth structure, such procedure has been necessary since fillings in non-undercut cavities would be subject to almost immediate failure.
The older types of dental filling materials, consisting of mercury amalgams, have a tendency to corrode at the interface with a tooth, and the corrosion products formed a seal preventing the ingress of saliva and decay-causing bacteria. However, the mercury and many of its corrosion products are themselves toxic and were also capable of having a deleterious effect on natural tooth material, so that this method of "sealing" the gap between filling and tooth was less than satisfactory. Amalgam fillings also suffered from excessive visibility and never matched the tooth color or surface texture.
Dental inorganic sealant and filling compositions, and the newer and more popular organic polymer filling materials, do not corrode and do not form strong and durable bonds to tooth structure. Therefore, indigenous oral and food-borne bacteria, together with saliva and the products of salivary digestion, easily invade the gap between these inorganic or polymeric sealant or filling compositions and the tooth material beneath it, leading in time to well-known secondary cariogenic processes with consequent eventual enlargement of the tooth cavity and the necessity to replace the filling or remove the tooth. Frequently inorganic filling materials utilize acidic curing agents, which produce trauma in the tooth structure and, hence, are undesirable from this point of view.
A recently introduced dental adhesive called polycarboxylate cement (aqueous polyacrylic acid and zinc oxide) has been shown to adhere efficiently to tooth enamel, but not to dentin. Reports of materials claimed to be capable of bonding adhesively or chemically to dentin are few, and include the following:
(1) Buonocoro, M., Wiloman, W., and Brudevold, F. A., Report on a Resin Composition Capable of Bonding to Human Dentin Surfaces, J. Dent. Res. 35:846-851, 1956. PA1 (2) Galligan, J. D., Schwarts, A. M. and Minor, F. W., Adhesive Polyurethane Liners for Anterior Restorations. J. Dent. Res. 47:629-632, 1968. PA1 (3) Buonocoro, M. G., Bonding to Hard Dental Tissues in `Adhesion in Biological Systems.` Rd. R. S. Manly, Academic Press, 1970, p. 225-254. PA1 (4) Khowassah, M. A., and Shippy, R. L., In Vitro Investigation of the Adhesive Strength of Cyanoacrylate Bonds to Human Hard Tooth Structures. J. Biomed. Mat. Res. 5 (1971) 159-168.